This invention relates to a vibration type liquid density meter which detects the density of a liquid by introducing the liquid into pipes, vibrating the pipes, and the measuring the natural frequency of the vibrating pipes.
One known vibration type liquid density meter comprises a high intensity magnet disposed in the vicinity of a pair of parallely disposed pipes and a current is applied to the pipes to cause their vibration by the Fleming's force thus generated. This device, however, is deficient in many ways. For example, magnetic powder existing in the liquid to be measured is attracted to the magnet and remains in the pipes. This increases the density of the pipes and causes errors in measurements. Moreover, the magnetic powder tends to wear down the pipe walls, and in extreme cases may cause holes in the pipe walls. Furthermore, the magnet and device structure are bulky and inconvenient to use.
Another known device is equipped with a pipe of magnetic material, and the pipe is vibrated by means of an electromagnet. But this device is also deficient in that the typesof liquid which can be measured are limited since a suitable magnetic material of high corrosion resisting property is not yet available. In addition, the device structure is bulky.
There is another known device with a piezoelectric element attached to the middle portion of a pipe. However, this device is deficient in that substantial measurement errors occur since the vibration characteristic of the pipe is varied by attachment of the piezoelectric element to the middle part of the pipe. The lead wires to the piezoelectric element periodically breaks down due to the simultaneous vibration of the piezoelectric element and the pipe.